An "early" and a "late" phase estrogenic response in the uterus has been recognized for more than 60 years yet mechanisms involved in their regulation remain controversial. One concept is that an early event(s), occurring within the first 6 h, prepares the uterus for later (18-30 h) increase in DNA synthesis, cell proliferation, and protein synthesis. An alternate view is that the late or growth phase is a result of the continuous presence of a stimulus. Discussion of either concept usually makes the assumption that all of the responses are dependent upon ligand interaction with one of the two estrogen receptor isoforms (ERalpha and ERbeta). However, increased gene expression following injection of estrogen or xenoestrogen, in mice lacking ERalpha, or in which all ER-activity has been suppressed by an estrogen-antagonist, ICI 182,780 (ICI), has shown this to be an oversimplification. Recently we identified several downstream target genes regulated early by estrogens in the uterus by an ER-independent mechanism. Preliminary studies indicated that estradiol-17beta (E2) rapidly activates phosphorylation of ERK1/ERK2 (MAP kinases) in uteri of both wild-type and ERalpha (-/-) mice. Furthermore, we observed that the administration of a selective inhibitor of ERK1/ERK2 activation (SL327), 30 min prior to an E2 injection totally abrogates the early responsive gene expression including uterine wet weights and the late uterotrophic (growth) responses. In contrast, injection of the inhibitor 6 h after E2 injection did not alter the late responses. Collectively, these results positioned us to study early and late estrogenic responses separately and determine the relationship between these two phases. Our hypothesis is that while estrogenic early responses are ER-independent, late responses are ER-dependent, and cooperation between the two phases is necessary for a full complement of estrogenic responses mediated by natural estrogen or xenoestrogen in the uterus. Our specific aims are to determine: 1. Early responses coordinate with the late growth responses for estrogenic actions in the uterus. 2. Molecular interactions of early and late estrogenic responses mediated by ER. 3. Direct consequences of inhibition of early genes in defining the estrogenic responses in uterine cells both in vivo and in vitro by adenoviral vector-driven delivery. 4. Estrogen-dependent early responsive genes function in a coordinated fashion to regulate ER-dependent activities. The results will help us define the relationship and a molecular cross-talk between the two-phase estrogenic responses in the uterus.